1. Field of the Invention
This invention relates to a film forming unit for forming a coating layer on a surface of a substrate.
2. Description of the Related Art
In the process for manufacturing semiconductor devices, for example, the photolithography process including resist coating processing for coating a resist solution on a wafer surface to form a resist layer, exposure processing for exposing to define a pattern on a wafer, developing treatment for developing the wafer having been exposed, and so on is performed with the respective processing devices to form a predetermined circuit pattern on the wafer.
In the above resist coating processing, the resist solution is discharged from a coating solution discharge nozzle toward above of the wafer. The coating solution discharge nozzle is contaminated by the resist solution and the like and thus needed to clean as necessary.
Conventionally, the coating solution discharge nozzle is cleaned with a cleaning fluid of solvent or the like such that a discharging port of the coating solution discharge nozzle is dipped into the solvent stored in a cleaning bath.
However, fine contamination cannot be perfectly removed by simply dipping as in the conventional manner. Furthermore, with recent advances in semiconductor technology, the desire to reduce a hole diameter of the aforementioned discharging port to approximately 200 xcexcm grows. On such a minute diameter, a high effectiveness of cleaning is not expected from the conventional cleaning method as described above, with the result that minute contaminations may remain on the above discharging port.
If contaminant is adhered even slightly on the discharging port of the coating solution discharge nozzle, a direction or pressure of discharging the resist solution is varied and thus the resist solution is not coated appropriately on the wafer, resulting in a possibility of forming no coating layer having uniform thickness.
Conventionally, as shown in FIG. 21, the resist solution stored in a resist solution reservoir 213 is sent into a flow channel by a press type pump 216 such as a bellows pump, passed through a filter 217 or the like, and then supplied from the above coating solution discharge nozzle 211 onto the surface of a wafer W. In this event, the resist solution 213 for, e.g. five wafers W is stored in the bellows pump 216, and the resist solution 213 for one wafer W is pushed out from the bellows pump 216 to be supplied from the nozzle 211 onto the surface of the wafer W.
The discharge pressure of the coating solution discharge nozzle exerts an influence upon the volume of resist solution supplied onto the wafer W as it is. Hence, in order to insure uniform film-thickness, the discharge pressure for the resist solution is required to keep approximately constant.
In a conventional supply system for the resist solution, when a long time, for example, around one minute is taken for discharge, it is difficult to maintain the discharge pressure at a constant value. This produces variation in the volume of resist solution supplied to the wafer W. As a result, the uniform film-thickness of the resist layer may become worse.
The present invention has been made in view of the aforementioned points, and it is a first object thereof to perfectly remove contamination adhered on a discharging port of a coating solution discharge nozzle even if the discharging port has a minute hole diameter, in order to form a preferred and uniform film of a coating solution on the surface of substrate. It is a second object of the present invention to form a film of a coating solution having a constant thickness by controlling variation in the volume of processing fluid discharged from a coating solution discharge nozzle onto a substrate.
To attain the first object, according to a first aspect of the present invention, a film forming unit of the present invention is a film forming unit for discharging a coating solution from a coating solution discharge nozzle toward a substrate to form a layer on a surface of the substrate, in which the coating solution discharge nozzle has a supply flow path for supplying a cleaning fluid to a discharge flow path continuing to a discharging port of the coating solution discharge nozzle.
In this way, by positively supplying the cleaning fluid directly to the discharge flow path of the coating solution discharge nozzle, the supply pressure of the cleaning fluid as well as the capability of cleaning is added. Therefore, further effective cleaning is attained in compare with the conventional case where a coating solution discharge nozzle is simply dipped into a cleaning fluid. In consequence, even when the discharging port of the nozzle is minute, it is possible to perfectly remove the contamination. This allows the discharge pressure to remain constant so as to form a uniform coating layer on the substrate.
When a supply port of the supply flow path opens toward the inside of the discharge flow path, the inside of the discharge flow path can be further effectively cleaned. If the discharge flow path has a water repellant finish against the coating solution, this causes hard adhering contamination on the discharge flow path, resulting in reduction in number of cleaning.
In the present invention, a store portion for the coating solution provided in a main body of the coating solution discharge nozzle and continuing to the discharge flow path; and an air-bubble removing apparatus removing air bubbles included in the coating solution and accumulating in an upper portion of the store portion may be provided.
A dissolved gas is typically included in the coating solution flowing in the store portion in some degree. The dissolved gas is vaporized by slight variation in pressure, and air bubbles occurs in the coating solution. If any measures is not taken against the air bubbles, the air bubbles gradually increase and is involved in the coating solution to be discharged from the discharging port, and coated on the substrate. Also, if the air bubbles accumulates in the store portion, the discharge pressure of the coating solution is varied due to compressibility of the air bubble, so that the coating solution is not discharged at a predetermined pressure. By providing the air-bubble removing apparatus, the air bubbles are removed and the above detriments are avoided. The air-bubble removing apparatus can be proposed as, for example, an apparatus capable of sucking air bubbles.
By providing an outlet pipe for letting out the air bubbles in the air-bubble removing apparatus, the above removing of the air bubbles is appropriately carried out. Since the coating solution flowing into the above store portion is sent at a predetermined pressure, the valve provided in the outlet pipe is closed except when the air bubbles are removed in order to have no effect on the discharge pressure of the coating solution. With a detector for detecting the air bubbles accumulating in the upper portion of the store portion, the removing of the air bubbles can be performed only when the air bubbles accumulates by a predetermined amount. The detector can employ a mechanism using variation in transmissivity of light. Also, it is possible to use a detecting member for detecting contamination on the coating solution discharge nozzle as image data.
When a diaphragm type pump for supplying the coating solution to the coating solution discharge nozzle is used, a detector for detecting changes in amount of push-on of the pump; and a cleaning controller for controlling the supply of the cleaning fluid by the supply flow path based on a detected result of the detection mechanism, may be provided. When the amount of push-on of the diaphragm type pump changes and the change is detected, based on the detected result, for example, the supply flow path is controlled when the detected value reaches a predetermined value, and after the coating solution discharge nozzle is moved to a predetermined position, the supply of the cleaning fluid to the nozzle is started. As a result, since the cleaning of the coating solution discharge nozzle can be performed only when the discharging port is contaminated, unnecessary extra cleaning works can be omitted. When a rotary type pump driven by electric power is used, a detector for detecting changes in rotation frequency or changes in electric power consumption of the pump can be employ.
To attain the second object of the present invention, according to a second aspect of the present invention, a film forming unit of the present invention includes: a press type pump including a pump body for sending the coating solution to the coating solution discharge nozzle, and a press member for pressing the pump body, the coating solution being sent into the pump body from the upstream by pulling the press member, the coating solution being sent from the pump body toward the downstream by pressing the press member, the amount of coating solution sent toward the downstream being adjusted by the amount of press of the press member; a pressure detector for detecting pressure in a flow path for the coating solution between the press type pump and the coating solution discharge nozzle; and a controller for controlling the amount of press of the press member of the press type pump based on a detected value from the pressure detector, in which the amount of press of the press member of the press type pump is controlled based on the pressure in the flow path for the coating solution between the press type pump and the coating solution discharge nozzle, to control the amount of discharge of the coating solution to be supplied from the coating solution discharge nozzle toward the surface of the substrate.
In the present invention, based on the pressure in the flow path of the processing fluid located between the press type pump and the discharge nozzle, the amount of press of the press member of the press type pump is controlled to allow the discharge pressure of the processing fluid to be supplied from the discharge nozzle toward the surface of the substrate to become constant. Therefore, the amount of discharge of the processing fluid remains invariant during the processing, resulting in forming a solution layer having a stable film thickness.
According to a third aspect of the present invention, a film forming unit of the present invention includes: a displacement gauge for detecting the amount of press of the press member of the press type pump; and a controller for controlling operation of an alarm generating portion based on a detected value from the displacement gauge, in which the alarm generating portion is operated when the amount of press of the press member of the press type pump goes out of a preset reference range. In this case, irregularities such as clogging of the discharge nozzle can be detected at an early stage, and it is possible to take an appropriate action. Hence, reset time period until forming of a stable solution layer restart is decreased.
According to a fourth aspect of the present invention, a film forming unit of the present invention includes: a displacement gauge for detecting the amount of press of the press member of the press type pump; a cleaning portion for cleaning the coating solution discharge nozzle; a drive mechanism for moving the coating solution discharge nozzle to the cleaning portion; and a controller for controlling operation of the drive mechanism based on a detected value from the displacement gauge, in which the coating solution discharge nozzle being moved to the cleaning portion by the drive mechanism for cleaning of the coating solution discharge nozzle when the amount of press of the press member of the press type pump goes out of a preset reference range. In this case, when the irregularity such as the clogging of the discharge occurs, the discharge nozzle can be quickly cleaned without putting any burden on an operator.
According to a fifth aspect of the present invention, a film forming unit of the present invention includes the coating solution discharge nozzle having a flow path for the coating solution; a discharging port connected to the flow path for the coating solution for discharging the coating solution in a line form having a very small diameter; and a filter provided to cross the flow path for the coating solution for removing air bubbles from the coating solution. In this case, variation in discharge pressure of the processing fluid which is caused by the presence of air bubbles included in the processing fluid, and the like are suppressed. This allows the stable supply of the processing fluid for the substrate, resulting in improving uniformity of a film thickness of a solution layer. In this point, it is desirable that the filter is made of a porous resin.